1. Field of the Invention
The present invention generally relates to a sustained release beneficial agent delivery system. More particularly, the invention relates to a sustained release beneficial agent delivery system having a capillary channel for controlling the rate of release of the beneficial agent by diffusion.
2. Description of the Related Art
Various dispensing systems for the delivery of active agents are known in the art. These systems generally deliver the active agent by diffusion from an enclosed capsule or from a multi-structured device having a wall formed of a polymer permeable to water and/or to the agent into a selected environment. See, e.g., U.S. Pat. Nos. 4,135,514; 3,760,806; 3,760,984; and 3,995,631. However, there is a large category of agents that cannot be readily delivered by such prior art systems because of at least one feature inherent in the devices which adversely affects the rate of release of the agent from the device. For example, many agents cannot be effectively delivered from a diffusion controlled delivery system because their permeation rate through the rate controlling material of the system is too small to produce a useful effect.
There is an additional class of active agents that also cannot be satisfactorily delivered by diffusional devices because of a particular chemical characteristic of the agent. This additional class includes salts that, because of their ionic character, will not readily diffuse through polymeric membranes. This class also includes unstable polar compounds that cannot be formulated into a satisfactory composition suitable for storage and delivery from such prior art systems.
In view of the above-mentioned disadvantages of prior art diffusional delivery systems and devices, there is a need in the art for a system that is capable of providing sustained delivery of beneficial agents, particularly, of beneficial agents that do not readily permeate through polymeric membranes.